Digital signal processing has become a mainstream technology employed by designers at the integrated circuit, board and system design levels. The technology is a core ingredient in many technology-related fields including the telecommunications and computer industries. For instance, many mobile phones, modems, digital versatile discs (DVDs), and a myriad of related products depend on digital signal processors (“DSPs”) for their basic functionality. DSPs are also effectively employed in audio, video and multimedia peripherals, disk drives and image processing systems for applications such as medical and scientific purposes. As further developments in the DSP technology occur, DSPs will be advantageously employed in a multitude of other applications.
Among the components found in conventional DSPs are signal filters. Employed to filter incoming data signals in a variety of ways, signal filters are being used in an increasing number of electronic devices. One commonly used type of signal filter is a finite impulse response (FIR) filter. A FIR filter is a sampled data filter characterized by its impulse response. Its input signal is a discrete time sequence which may be analog or digital. The output of the FIR filter is also a discrete time sequence, and is the convolution of the input sequence and the filter impulse response based on predetermined coefficients. FIR filters may be implemented in the analog domain or in the digital domain.
Typically, FIR filters used in “upsampling” incoming signals not only boost the signal, but may also average the signal to arrive at the appropriate output signal. Unfortunately, many of the logic devices, such as “adders”, in conventional FIR filters operate at the faster clock rate of the upsampled signal in order to provide an accurate frequency response. However, such logic devices designed to operate at these higher frequencies are typically more costly than those that operate at lower frequencies, such as the frequency of the input signal. In addition, those skilled in the art understand the increased power consumption of an FIR filter whose logic devices are operated at such an increased clock rate.
Accordingly, what is needed in the art is a filter circuit that can provide a sampled signal based on an input signal that does not suffer from such deficiencies.